Wireless transceivers conserve space within wireless devices by having the transmitter and receiver share an antenna. Generally, the transceiver isolates the transmitter and receiver by including a circulator and/or other switching mechanism between the transmitter and receiver. The switching mechanism connects the transmitter to the antenna while isolating the receiver from the transmitter and antenna when the transceiver transmits signals, and connects the receiver to the antenna while isolating the transmitter from the receiver and antenna when the transceiver receives signals from the antenna.
Because wireless receivers are typically designed to amplify and process very small energy signals, such receivers are susceptible to damage caused by high energy signals. For example, electrostatic discharge (ESD) comprises high energy signals that may damage the receiver. Further, the performance of the receiver may be degraded by undesirable signals that leak into the receiver when the receiver is inactive. Thus, it is desirable to isolate the receiver from damaging high energy signals during all operating modes and from undesirable signals, e.g., a transmission signal reflected by the antenna into the receiver, when the receiver is inactive.
The switching mechanisms in conventional transceivers are generally designed to isolate the disconnected element, e.g., the receiver, from the connected elements, e.g., the transmitter. Further, the transceiver may include filters designed to further suppress signals outside the receiver frequency band. Unfortunately, such isolation and suppression techniques generally do not sufficiently suppress ESD signals. Further, because some communication standards specify overlapping transmit and receive frequency bands (see Table 1), some transmission signals are in the receiver frequency band, and may therefore leak into the receiver when the receiver is inactive. Unwanted RF energy that leaks into the receiver during transmission and/or idle operating modes degrades the receiver performance (sensitivity, noise figure, linearity, etc.).
TABLE 1StandardTX Band (MHz)RX Band (MHz)DCS 18001710-17851805-1880PCS 19001850-19101930-1990
U.S. Patent Publication 2009/0264084, herein referred to as the '084 publication, discloses one exemplary device and method for addressing these problems. In this application, a pair of diodes connected in anti-parallel are disposed between the switching mechanism and the receiver. When kept at a zero bias, the anti-parallel diodes provide general ESD protection for the receiver. Further, when the receiver is inactive, one of the diodes may be forward biased to produce a low ohmic switch to ground to prevent any signals, including unwanted RF energy, from passing into the receiver. While the solution of the '084 publication addresses the receiver problems resulting from high energy signals and/or undesired leakage signals, the size of the diodes and the parasitics associated with the diodes may be undesirable or unsuitable for some applications.
The Background section of this document is provided to place embodiments of the present invention in technological and operational context, to assist those of skill in the art in understanding their scope and utility. Unless explicitly identified as such, no statement herein is admitted to be prior art merely by its inclusion in the Background section.